Pigments are known to have wide applications in human life such as coatings, paints, papers, adhesives, latexes, toners, textiles, fibers, plastics, cosmetics and inks. When the white light of 380 or 400 nanometers to 760 or 780 nanometers encounters a pigment, a part of spectrum is absorbed by the conjugated chemical bonds and other components present in the pigment. Other non-absorbed part is reflected or scattered. The reflected or scattered wavelength imparts color to the pigment. This knowledge of absorption and reflection by a particular chemical compound is being used to develop the variety of pigments.
A large number of organic and inorganic yellow pigments are available. They differ by their brightness of shade, opacity, fastness requirements, physiological properties, and economic considerations. These properties influence the choice of the pigments depending on the end application. As well as being used in yellow paints, yellow pigments are also used in oranges, greens and browns. Quinophthalone pigment is an organic yellow pigment used as a chrome replacement in high quality finishes. Quinophthalone pigment is prepared from quinaldine compounds.
Co-pending application 2990/MUM/2011 discloses new bis-quinaldine compounds.
German Patent 429176 discloses a process of preparing mono quinophthalones by reacting 3-hydroxy quinaldine with anhydride or imide of dicarboxylic acid followed by either halogenation or sulphonation reaction at 3-hydroxy position.
U.S. Pat. No. 5,106,980 discloses a process of preparing mono quinophthalones by condensing 8-aminoquinaldine with an optionally substituted phthalic anhydride in presence of molten benzoic acid as diluent at a temperature ranging between 123° C. to 200° C.
A method for preparation of bis quinophthalones having hydrogen or chlorine or methyl substituent at 8-position is disclosed in an article titled “Study on Quinophthalone Pigments”, Shikizai Kyokaishi, 44 (1971), 316-324. The method includes reacting fused phthalic anhydride with 6,6′-bis quinaldine and heating at 170° C. to 180° C. for 6 hours to 12 hours.
However, Bis-quinophthalones disclosed in Shikizai Kyokaishi, 44 (1971), 316-324, shows remarkable color fading when exposed for longer hours and are poor light resistant.
The mono-quinophthalone and bis-quinophthalone of the prior art typically, suffer from drawbacks such as poor light resistance, poor solvent resistance, poor hue and less stability.
Thus, there is felt a need to develop new bis-quinophthalone pigments which can obviate the drawbacks associated with the prior art.